[R] Contrasts

[Kimberly Ann Fernandes]

Hello,

I am trying to figure out how to conduct a t-test on a specific contrast
for my data.  I have four factors in my data and would like to conduct a
t-test on the average of the data from the first two factors against the
average of the data on the second two factor (i.e. is the average of the
first two different from the average of the second two).  Is there a
quick way to do this?  I found the contrast function, but wasn't sure
how to apply it.

Thank you,
Kim